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Temporary plugging agents (TPAs) are widely used in oilfield development due to their self-removal after operations and their minimal effect on reservoirs. However, the current methods used to remove TPAs may damage the reservoir. To address this, a self-degradable TPA for 120 °C conditions was prepared and tested in this study. Using acrylamide (AM) as the base monomer, along with polyethylene glycol diacrylate (PEGDA) and N,N′-methylenebisacrylamide (MBA) as crosslinkers, a crosslinked shell was synthesized. The degradation time of this shell can be adjusted by changing the ratio of two crosslinking agents. The shell served as a shielding layer to encapsulate polylactic acid (PLA), thereby delaying the latter's degradation. Experimental results confirmed that the TPA had a core–shell structure and exhibited good compatibility with base slurry. At a concentration of 0.5%, it effectively reduced filtration volume of base slurry. Furthermore, the TPA showed favorable plugging performance and pressure-bearing capacity. As the ratio of the two crosslinking agents varied, the water absorption capacity of the TPA exhibited an increasing trend, and its degradation duration at 120 °C ranged from 60 to 72 h. FT-IR and SEM analyses revealed structural changes of the TPA in the degradation process. All test results demonstrated that degradation primarily occured through the cleavage of amide and ester bonds, leading to the rupture of crosslinking points.